The present invention relates to method and apparatus for the calibration of radiant energy detection apparatus. The invention finds particular application and will be described with particular reference to ultrasonic apparatus for detecting flaws in pipe and tubular goods. It is to be appreciated, however, that the invention also finds application in the calibration of inspection equipment useful in conjunction with other articles, particularly elongated or continuously formed articles including bars, rods, beams, sheets, and the like. In addition to ultrasonic flaw detection systems, the invention may also find utility in the calibration of other reflective and non-reflective radiant energy scanning systems.
Heretofore, the calibration of ultrasonic flaw detection systems has included positioning an ultrasonic transducer adjacent to each of a plurality of preselected, known flaws and monitoring the responses. Most commonly, each known flaw was a bored, flat bottomed hole of known depth. When monitoring each preselected flaw, the ultrasonic detection system was expected to produce a corresponding preselected, known response. Conventionally, the ultrasonic detection system included a gain adjustment and a distance amplitude correction adjustment. If the actual response of the ultrasonic detection system varied from the corresponding preselected response, the gain and distance amplitude correction adjustments were varied until the actual response matched the preselected response. The next transducer was then positioned adjacent the flaws and its gain and distance amplitude correction were similarly adjusted. When calibrating an array of ultrasonic transducers, a plurality of substantially identical sets of flat bottom holes could be provided, one set for each transducer. However, it would be difficult and labor intensive to provide flat bottom holes of exactly the same size and depth. Further, it would be difficult to position all of the holes precisely in the same relative position to its corresponding transducer. Any deviation in the size or location of a hole would create an error in the calibration of the corresponding transducer and degrade the accuracy of the results.
Commonly, pipe for oil well drilling, pipe and tubing for nuclear plants, and the like were tested for flaws at the steel mill and again in the field at the installation site. The physical movement of the inspection apparatus between installation sites as well as changes in temperature, humidity, altitude or barometric pressure, and the like necessitated regular recalibration of the inspection apparatus. Heretofore, the pipe has been inspected with gamma rays, electromagnetic fields, and other forms of penetrating radiant energy. The degree of attenuation of gamma radiation passing from a radiation source inside the pipe to one or more radiation detectors on the outside of the pipe provided an indication of flaws, concentricity, wall thickness, and other pipe characteristics. Variations in a magnetic field through which a metal pipe was passing provided an indication of variations in the magnetic susceptibility of the pipe caused by flaws and the like. Ultrasonic detection systems were commonly used in conjunction with the gamma ray and electromagnetic flaw detectors. Specifically, any area possessing a possible flaw was denoted or marked during gamma radiation or electromagnetic examination. Thereafter, an inspector using a hand held ultrasonic probe inspected the denoted area. In this manner, the ultrasonic probe provided a more detailed indication of the flaw initially detected by the relatively coarse gamma ray or electromagnetic flaw detector.
One of the problems with gamma radiation and electromagnetic pipe flaw detectors is that they are relatively insensitive to small flaws. This tends to degrade their ability to determine the exact position and nature of a detected flaw. The use of a hand held ultrasonic probe to more accurately examine the nature and position of a flaw is relatively slow and labor intensive.
The present invention contemplates a new and improved flow detection calibration method and apparatus for radiant energy detection systems.